The present invention relates to an apparatus and a method for bonding two semiconductor laser chips at narrow pitches on one submount in high accuracy. The present invention is utilized in an apparatus for bonding the two laser chips (for example, combination of a red chip and an infrared chip or the like) such as a combination laser die-bonder or the like.
One example of a conventional one-chip bonding apparatus is explained below. Conventionally, a semiconductor laser chip 4 is vacuum-sucked by using a vertically provided vacuum-suction collet 6, peeled from a wafer sheet 1, transferred to an intermediate stage 2 and passed as shown in FIGS. 1 and 2. On the intermediate stage 2, a chip profile is recognized by image processing and then, a light-emission axis is recognized. A chip position is corrected in X, Y and xcex8 directions on the basis of this data.
After the chip position is corrected in the X, Y and xcex8 directions on the intermediate stage 2, the chip is sucked again by using the suction collet 6 and transferred onto a submount 5 placed on a bonding stage 3. The chip is bonded onto the submount 5 as it is with an adhesive or by thermo-compression bonding.
That is, the chip position is corrected only on the intermediate stage in the above-described conventional one-chip bonding apparatus. Therefore, when the chip is passed to the submount by using the collet after the position correction on the intermediate stage and the chip is mounted on the submount, a fine shift occurs. Thus, bonding position accuracy according to a specification (xc2x12 xcexcm or less) could not be ensured, thereby resulting in variations in a laser direction.
A method of efficiently fabricating a semiconductor laser without variations in a light-emitting direction in a die-bonding process of a semiconductor laser is disclosed in Japanese Patent Laid-Open Publication No. 7-202347. In this method, a laser chip is energized and allowed to emit light on the intermediate stage by using a probe. A light-emission axis direction is measured by image processing and the laser chip position is corrected on the basis of the measured value. When the light-emission axis direction is within a certain error range, the laser chip is sucked and transferred by a laser chip feed mechanism for die-bonding. Thus, the chip position accuracy is improved.
When a two-chip semiconductor laser device is fabricated, two kinds of light-emitting chips having different wavelengths are bonded on one submount with favorable accuracy. The chips 12, 13 are bonded one by one in FIG. 3A. When the second chip 13 is bonded, heat is applied to the first already bonded chip 12 at its junction and the clip 12 comes off. Therefore, the two chips need to be bonded at the same time.
In FIG. 3B, two conventional collets are simply arranged in a mirror image to constitute a two-chip bonding by using the one-chip bonding apparatus in FIG. 2 so that two laser chips are die-bonded on a submount.
Since a specification for a distance between light-emission points is 100xc2x12 xcexcm in the two-chip semiconductor laser device, the chips need to be bonded so that a distance between the respective light-emission points 14, 15 of the two laser chips 12, 13 is 100xc2x12 xcexcm as shown in FIG. 4. It is shown, however, that, since the collets are vertically disposed in a constitution shown in FIG. 3B, the collets interfere with each other and thereby the two chips cannot be bonded closely.
In the method disclosed in Japanese Patent Laid-open Publication No. 7-202347 as well, it is shown that, since the collets are vertically disposed, the collets interfere with each other and thereby the two chips cannot be bonded closely.
To prevent the collets from interfering with each other in the constitution where the collets are vertically disposed, a diameter of the main body of a collet might be made thinner than the chip profile. However, currently the diameter of the main body of the collet cannot be made thinner than the chip profile because a vacuum hole for vacuum-sucking a chip needs to be provided, rigidity larger than a certain level is required due to a load applied upon chip suction and chip bonding and the collet needs to be shaped so that position accuracy in attachment/replacement of the collet can be easily ensured.
As described above, when the above conventional devices are simply arranged laterally in a mirror image when a semiconductor laser device in which two laser chips are die-bonded on a submount is fabricated, there are disadvantages described below.
(1) Since the position is corrected only on the intermediate stage, a fine shift occurs after the correction on the intermediate stage when the chip is passed by using a collet or the chip is placed on the submount.
(2) The specification required distance (x in FIG. 4) between the light-emission points of the two chips is as narrow as 100 xcexcm. Therefore, when the two chips are bonded at the same time, the normal vertical collets interfere with each other and thereby the two chips cannot be bonded at desired positions at the same time even if the light-emission point is positioned as closely to an end of the chip as possible.
The present invention was accomplished from the above viewpoints. Accordingly, an object of the present invention is to provide an apparatus and a method for bonding two semiconductor laser chips on one submount at narrow pitches in high accuracy.
In order to achieve the above object, there is provided a method of fabricating a semiconductor laser device wherein two semiconductor laser chips are die-bonded on one submount, comprising processes of placing the semiconductor laser chips on intermediate stages, allowing the semiconductor laser chips on the submount to emit light and measuring light-emission point positions and transferring the semiconductor laser chips through fixed points to prescribed positions on the submount.
That is, in the present invention, a position of each semiconductor laser chip is corrected by profile recognition and light-emission axis recognition on the intermediate stage, a voltage is applied to each chip by using a collet as an electrode on a bonding stage for bonding the chip on the submount to allow each of the two chips to emit light, the light-emission point position data is subjected to image processing, the position of each of the two chips is finally corrected by a high-resolution precision positioning mechanism driven by a piezo-electric element of a bonding head on the basis of the data and then bonding is performed. Thus, according to the fabricating method of the present invention, a two-chip semiconductor laser device can be fabricated in high bonding accuracy.
In one embodiment of the present invention, the method comprises a process of measuring light-emission point positions and light-emission axis directions of the semiconductor laser chips placed on the intermediate stages.
In one embodiment of the present invention, the method comprises a process of correcting positions and directions of the intermediate stages on the basis of the results of measuring the light-emission point positions and light-emission axis directions of the semiconductor laser chips placed on the intermediate stages.
In one embodiment of the present invention, the method comprises processes of sucking the two semiconductor laser chips from respective wafer sheets or a chip tray by using collets, transferring the collets through fixed points by a fixed-point transfer movement mechanism and placing the two semiconductor laser chips on the respective intermediate stages, correcting positions of the two semiconductor laser chips on the respective intermediate stages, sucking the two semiconductor laser chips again, transferring the chips through fixed points and mounting the chips on the submount, energizing the two semiconductor laser chips on the submount to allow the chips to emit light and measuring a distance between the light-emission points of the two chips.
In one embodiment of the present invention, the method comprises a process of transferring the two semiconductor laser chips onto the submount through fixed points and then correcting the chip positions on the basis of the measured distance between the light-emission points by a movement mechanism for fine XY movement provided separately from the fixed-point transfer movement mechanism.
Therefore, according to the present invention, two chips are once placed on respective intermediate stages, a profile and a light-emission axis of each chip are recognized by a camera, the chip position is corrected by image processing and the chip whose position is corrected is transferred onto a submount through fixed points from left and right. Therefore, a shift on the submount occurs only when the chip is passed after the profile recognition. Therefore, light-emission points of the two chips can be easily recognized even in a narrow visual field of a high-magnification camera.
When the chip position is not corrected on the intermediate stage, the two chips may hit each other due to a large shift upon pickup of the chips since the gap between the two chips is narrow. However, this can be prevented.
Since the distance between the light-emission points of the two chips on the submount is measured to confirm that the chips are at prescribed positions and then thermo-compression bonding is performed, bonding can be performed in high accuracy.
That is, according to the present invention, positions of the two semiconductor laser chips are corrected on the intermediate stages by image processing. Since the distance between light-emission points of the two semiconductor laser chips is further measured on the submount to correct the positions, bonding can be performed with a more accurate distance between the two chips as compared with a conventional method wherein the chip position is corrected only on the intermediate stage.
When no problem occurs upon the above-described pickup of the chip, the position can be roughly corrected on the intermediate stage. Consequently, a process time can be shortened on the intermediate stage so that the apparatus tact can be shortened.
In one embodiment of the present invention, the method comprises processes of allowing the two semiconductor laser chips to emit light on the submount at the same time, measuring a distance between light-emission points and using one light-emission point as a reference and moving the other chip to a prescribed position on the basis of the measurement data.
According to the above embodiment, bonding can be performed accurately and the apparatus can be constituted at a relatively low cost, since only one chip bonding head needs to have a fine adjustment mechanism.
In one embodiment of the present invention, the method comprises a process of allowing the two semiconductor laser chips to emit light on the submount, measuring a distance between the light-emission points and moving both the chips to prescribed positions by using light-emission point positions predetermined for both the semiconductor laser chips as references on the basis of the measurement data.
According to the above embodiment, bonding can be performed accurately and, by providing both the chip bonding heads with a fine adjustment mechanism, not only a relative position between the two chips, but also an absolute position of each laser chip with respect to the submount can be determined in high accuracy.
Also, there is provided a two-chip bonding apparatus for die-bonding two semiconductor laser chips on one submount, having intermediate stages for correcting positions and directions of the semiconductor laser chips, a bonding stage for placing a submount on which the semiconductor laser chips are bonded, means for allowing the two semiconductor laser chips to emit light at the same time on the submount placed on the bonding stage, means for measuring a distance between light-emission points of the two semiconductor laser chips and means for transferring the two semiconductor laser chips through fixed points to prescribed positions on the submount.
In one embodiment of the present invention, the apparatus has collets for sucking the semiconductor laser chips, a fixed-point transfer movement mechanism which is connected to collet heads of the collets to move the collets, means for recognizing profiles of the semiconductor laser chips on the intermediate stage, means for recognizing light emission axes of the semiconductor laser chips on the intermediate stages, a drive mechanism for correcting positions and directions of the intermediate stages, means for allowing the two semiconductor laser chips to emit light at the same time on the submount placed on the bonding stage and means for measuring a distance between light-emission points of the two semiconductor laser chips, and which corrects positions of the two semiconductor laser chips on the submount and then performs bonding.
The conventional collets are vertically disposed as shown in FIGS. 1 and 2. On the other hand, in the present invention, the collets are disposed while tilted towards both the front and lateral directions of the device as shown in FIG. 5A so that the collets do not interfere with each other upon die-bonding of two chips. Thus, die-bonding can be performed in favorable accuracy with a gap between the light-emission points of 100 xcexcm.
Therefore, a tilted-type collet 16 whose end is ground so as to be in parallel to the chip surface was developed in the present invention so that a chip could be sucked while the collet is tilted. FIG. 6 shows an enlarged view of the end portions of the tilted-type collets of the present invention.
In such an eccentric-type collet 17 as shown in FIG. 5B, die-bonding can be similarly performed in favorable accuracy with a gap between the light-emission points of 100 xcexcm. This eccentric-type collet 17 is obtained by soldering an eccentric block to a conventional collet to deviate the collet end from the center. Thus, collets are prevented from interfering with each other.
In one embodiment of the present invention, a piezo-electric element precision drive mechanism for fine XY movement is separately connected to the collet heads separately from the fixed-point transfer movement mechanism.
According to the above embodiment, in each of the bonding heads for a red chip and an infrared chip, a precision positioning mechanism (a piezoelectric element precision drive mechanism is further provided on a block driven by a ball screw in the XY direction and the collet is disposed at its ends.
In one embodiment of the present invention, the piezo-electric element precision drive mechanism is driven on the basis of the measured light-emission point distance data.
In one embodiment of the present invention, the collets are tilted-type collets, the two tilted-type collets are attached as opposed to each other and the two semiconductor laser chips can be die-bonded at the same time by using the two tilted-type collets.
According to the above embodiment, the two respective semiconductor laser chips can be made close to each other while vacuum-sucked. Thus, two-chip die-bonding with a fine gap can be achieved.
That is, in the two-chip bonding apparatus according to the present invention, chips are transferred through fixed points onto the submount by using the opposed tilted-type collets 16 shown in FIG. 5A and the chips are allowed to emit light on the submount. Each position is corrected by using a piezo-electric element on the basis of the light-emission point recognition data. Thus, die-bonding can be performed by the two collets in favorable accuracy.
In one embodiment of the present invention, a visual field is opened by using the opposed tilted-type collets as the collets so that a chip bonding state and a collet suction state can be confirmed from right above the chip bonding head.
According to the above embodiment, when the collets of the present invention are used, a bonding state can be confirmed from right above. The positions or bonding situations of the two chips can be monitored by disposing the camera right above the chips.
In one embodiment of the present invention, the collets are eccentric-type collets, the two eccentric-type collets are attached as opposed to each other and the two semiconductor laser chips can be die-bonded at the same time by using the two eccentric-type collets.
According to the above embodiment, the two semiconductor laser chips can be made close to each other while vacuum-sucked. Thus, die-bonding of two chips with a fine gap can be achieved.
That is, in two-chip bonding apparatus according to the present invention, chips are transferred through fixed points onto the submount by using the opposed eccentric-type collets 17 shown in FIG. 5B and the chips are allowed to emit light on the submount. Each position is corrected by using a piezo-electric element on the basis of the light-emission point recognition data. Thus, die-bonding can be performed in favorable accuracy by the two collets.
Therefore, according to the above constitution of the present invention, the resolution for positioning during the fixed-point transfer may be lower than a resolution required in the final position correction. The collets can be moved at a high speed during the fixed-point transfer. Thus, production efficiency can be improved.
When a position resolution is required in the final position correction between the two light-emission points on the submount, a high-resolution and accurate positioning can be achieved by a piezo-electric element.
In one embodiment of the present invention, a pair of collets are provided for each of the intermediate stages and the bonding stage.
According to the two-chip bonding apparatus of the present invention, since a pair of collets are provided both for the intermediate stage and the bonding stage, position correction on the intermediate stage and position correction on the bonding stage can be performed at the same time. Thus, the apparatus tact can be shortened.
To allow a chip to emit light, a probe needs to be brought into contact with the chip surface. In a conventional device, however, it was hard due to a small size of the chip to allow the laser chip surface to be brought into contact with a probe while the chip is being vacuum-sucked by a collet. However, when the collet is made with an energizing material and the collet itself is made with an energizing electrode, the laser chip can be energized and allowed to emit light while vacuum-sucked.
Therefore, in the two-chip bonding apparatus of the present invention, the collet is fabricated with an energizing material and used as an electrode for allowing the chip to emit light. The chip is allowed to emit light by applying a voltage to the collet.
According to the present invention, the collet is lowered while a laser chip is vacuum-sucked and mounted on the submount. The suction collet and the ground side on the submount can be energized so that the chip is allowed to emit light.
In one embodiment of the present invention, the collets are fabricated with a tungsten cobalt carbide (WCxe2x80x94Co) superhard metal sintering material, the collets are used as chip light-emitting electrodes and the chips are allowed to emit light by applying a voltage to the collets.
According to the above embodiment, since the collet is used as a tool for subjecting the semiconductor laser chip to thermo-compression bonding and as an electrode, the collet needs to have low thermal conductivity and high electric conductivity as well as high component rigidity and high component accuracy. Therefore, the inventors of the present invention paid attention to a WCxe2x80x94Co superhard metal sintering material as a material of the collet.
A WCxe2x80x94Co superhard metal sintering material has low thermal conductivity. Since heat does not easily escape through the collet upon thermo-compression bonding of the laser chip, this material is effective as a material of the collet. Due to relatively favorable electric conductivity, this material can also be used as an electrode. Furthermore, since the WCxe2x80x94Co superhard metal sintering material has high rigidity, a fine component having high accuracy and high rigidity can be fabricated by electric discharge machining.
Bonding in higher position accuracy could be achieved by using the method and the apparatus of the present invention as compared with a conventional die-bonding apparatus where chip correction is performed by image processing only on the intermediate stage.
That is, according to the present invention, when two semiconductor laser chips are die-bonded on one submount, the chips can be mounted in high accuracy with a distance between light-emission points of the two chips within a range of 100xc2x12 xcexcm Furthermore, since final position correction is performed on the submount, collets can be moved at high speed during fixed-point transfer. Thus, productivity can be improved.